Enhancement of gellan production in Sphingomonas paucimobilis JLJ by heterogeneous expression of Vitreoscilla hemoglobin

Abstract

A heterologous expression of Vitreoscilla hemoglobin (VHb) for improving cell growth and fermentation products has been successfully demonstrated in various hosts. To improve a commercially used strain for gellan, vgb gene was expressed in Sphingomonas paucimobilis JLJ under the control of the oxygendependent vgb gene promoter (P vgb). The promoter was maximally induced under microaerobic conditions. Biochemical activity of expressed vgb was confirmed by PCR, SDS–PAGE, and the CO-difference spectra analysis which exhibited a characteristic absorption maximum near 420 nm. The results showed that the expression of vgb could enhance cell growth. The composition of fermentation medium and the physical conditions of cultivations were investigated. The optimum medium consists of g/L): Sucrose 30, Soybean meal 5, NaNO 3 1, KH 2 PO 4 1, K 2 HPO 4 1.5, MgSO 4 0.6. The optimum fermentation conditions were confirmed: pH 6.0, seed age 16 h, inoculum volume 10%, 200 rpm, 30 °C, and the maximum gellan yield of vgb+ recombinant was 1.713% ± 0.02% after cultivated 72 h, 21% higher than that of the parental strain. VHb exhibited positive effect on cell growth and optimize gellan yield. The results provided potential applications of vgb gene in other industrially important strains to solve the increasing demand of aerobic processes in polysaccharides production.